The present invention relates to an integrated pressure sensor and a method for manufacturing an integrated pressure sensor. More specifically, an integrated pressure sensor fabricated using micro-electro-mechanical systems (xe2x80x9cMEMsxe2x80x9d) process is provided in a structure, which may also include devices created by a complementary metal oxide semiconductor (xe2x80x9cCMOSxe2x80x9d) process.
Surface and bulk micro-machined pressure sensors are known in the art (see, e.g., the SMD082 pressure sensor manufactured by the Robert Bosch Corporation, which is a bulk micro-machined pressure sensor system). Using similar technologies to those used to manufacture semiconductors, microscopic capacitors may be fabricated on silicon wafers. In certain applications, a capacitor may then be used for measuring pressure. For example, pressure applied to one electrode of the capacitor will cause it to deflect towards the other electrode of the capacitor resulting in a change in capacitance. The technologies for manufacturing capacitors on silicon wafers may include oxidation of a substrate, application of a photoresist material, selective exposure to light or x-rays through a mask, and etching to build devices in layers on a substrate.
Although similar techniques are used for creating integrated circuits (xe2x80x9cICsxe2x80x9d) and micro-electro-mechanical devices (xe2x80x9cMEMsxe2x80x9d), when both ICs and MEMs are constructed on the same substrate, elements of these processes can interfere with each other. For example, polishing and etching processes used in the manufacture of ICs may damage MEMs that have already been created on a silicon wafer. In addition, subjecting certain MEMs to high temperatures used for processing and building MEMs can damage or destroy the CMOS circuits. Cutting or xe2x80x9cdicingxe2x80x9d of a silicon wafer can also damage MEMs as stray particles can destroy a MEMs structure.
One solution for protecting a MEM during circuit creation and wafer processing has been to cover the MEM device with a protective layer (e.g., a layer of silicon oxide) during the processing stages in which the circuitry is created and the wafer is diced. This protective layer must later be removed in a time-consuming process. Furthermore, it is difficult to remove the protective layer without damaging the electronics components, and therefore the types of electronics that can be developed are limited.
In other known pressure sensor systems, the pressure sensor and the supporting circuitry are separately made in a so-called back-end integration process. In one known process, two piezoelectric resistors are formed in the substratexe2x80x94one towards the bottom of the substrate, one towards the top of the substrate. A relatively thick silicon dioxide exists below the second piezoelectric element. During the xe2x80x9cback-endxe2x80x9d processing a Potassium Hydroxide (KOH) etch is performed to create an open volume over the second piezoelectric resistor. If this open volume is evacuated, then the resistance of the second piezoelectric resistor will be related to the pressure in a vacuum. The pressure applied to the top of the substrate affects the resistance of the first piezoelectric resistor. The difference between the resistances of the first and second piezoelectric resistors may be used to provide a measurement of pressure.
Whether MEMs are developed first on a wafer and ICs are later developed, or the other way around, adding and later removing a protective covering for the first-developed components is generally required. These extra steps add time and expense to the process. Furthermore, in prior art processes, adding protective layers to cover components may be required to make the surface of the wafer approximately flat so that other operations such as etching and lithography may be performed.
These limitations have restricted the development of devices that include both MEMs and ICs. Such devices may include, for example, a pressure sensor including a capacitor and supporting circuitry.